This invention relates to sewage disposal apparatus and is particularly directed to a pneumatic sewage ejector for receiving sewage from one or more sources and for pneumatically pumping the received sewage into a main sewage pipe for further disposal.
In collection and disposing of sewage it is often desirable to collect the sewage over a period of time and then pump the sewage into a main sewage pipe when the collected sewage reaches a predetermined level. Such collection and subsequent pumping of the sewage avoids the necessity of continuously pumping sewage which is intermittently generated.
Systems have long been used whereby the intermittently generated sewage is collected in a tank until the sewage reaches a predetermined level. Upon reaching the predetermined level, air is blown into the tank under pressure to force the sewage out of the tank and into a main sewage discharge pipe through which it continues to a location of ultimate treatment.
Such pneumatic ejection of the fluid sewage is thought to be superior to systems involving electric pumps for expelling the sewage from the tank since pneumatic ejection can be accompanied by simultaneous aeration of the fluid sewage. This aeration of the sewage dissolves oxygen in it and substantially reduces the bacterial oxygen demand of the sewage, thereby reducing the development of septic and acidic conditions in the sewage.
Some prior pneumatic sewage ejectors have been controlled electrically; e.e., they contained one or more electrodes which extended into the tank to a predetermined depth. When the level of the sewage increased in the tank and finally reached the electrodes, a conduction path was created between the electrodes, the sewage, and appropriate control circuitry which energized a compressor for forcing pressurized air into the tank and driving the sewage out of the tank.
A difficulty with such electrically controlled ejectors is that the electrodes which extend into the tank tend to become corroded and coated with matter present in the sewage. Eventually, the conduction path through the electrodes, the sewage, and the control circuitry may tend to become intermittent, thereby inhibiting the proper operation of the ejector. Some other prior pneumatic sewage ejectors have been controlled by one or more floats in the tank which are connected to a rod which extends through a stuffing box to an air valve outside the tank. As the floats rise and fall in response to the level of fluid in the tank, the rod actuates the air valve to either admit pressurized air into the tank to expel fluid or to vent the tank to the atmosphere to allow fluid to enter the tank. A disadvantage of this type of sewage ejector is that the stuffing box can be a source of air leaks and is frequently a cause of premature failure of the ejector.